The invention relates to a glazing having a data transmission window.
Glazings are known comprising an electrically conductive coating. For example, an electrically conductive coating in a windshield may reflect infrared radiation, to prevent rapid heating of an interior of a vehicle by the sun, or may carry electric current for heating the windshield resulting in demisting or defrosting.
A known problem with such electrically conductive coatings is that transmission of communication signals is at least partly blocked. A windshield having an electrically conductive coating would at least partly block transmission of data for a navigation device (GPS), a mobile telephone or a toll collection device so these devices would not function in a vehicle fitted with the windshield. Therefore it is desirable to provide a means to allow transmission of a predetermined frequency of electromagnetic radiation through a windshield having an electrically conductive coating.
EP0531734B1 (Central/Nakashima) discloses a laminated panel, comprising a layer which is relatively high in reflectance for radio waves, said layer being divided into a plurality of segments by a series of slits. In a preferred embodiment, the width of each segment is 1/30 of the wavelength selected for transmission, whereby the reflectance of said layer for said radio wave is reduced. For example, to allow transmission of a signal of frequency 200 MHz (wavelength 1,500 mm) a width of each segment is 50 mm.
DE19508042A1 (NSG/Tsuno) also discloses an electrically conductive coating for transmission of electrical signals and reflection of heat, being divided into a plurality of segments by a series of slits, such that a width of each segment is less than 1/10 of the wavelength selected for transmission. For example, for transmission of a signal of frequency 2 GHz, a width of each segment is preferably less than 1 cm.
Both EP0531734B1 and DE19508042A1 provide an electrically conductive coating which is not electrically heatable, because it is divided into segments.
EP1559167B1 (AGC/Roquiny) provides a vehicle glazing panel, comprising a radiation-reflective coating layer and a window in the coating layer permeable to electromagnetic radiation. Typical electromagnetic wave frequencies are, for example, 88-108 MHz, 540-1650 kHz, 150-280 kHz, for radio signals; 890-960 MHz, 1710-1880 MHz, 1900-2170 MHz for mobile phone communications; 1575.42+/−10 MHz for GPS; and 5.8 GHz for Dedicated Short Range Communications (DSRC), such as toll collection. The window is a zone wherein the coating layer is absent from a pattern of dots. The dots form uncoated apertures in the coating layer and are arranged linearly or in alternate rows. Each dot has a diameter between 5 and 7 mm. The pattern of dots may increase the directivity of the transmission by focussing the signal, i.e. transmission through the pattern of dots can be greater than through a reference windscreen without a coating layer. The vehicle glazing panel may also be heated. The pattern of dots without coating allows the glazing panel to be heated substantially uniformly. Hot spots which may damage the coating layer are avoided. A disadvantage is that solar performance is sacrificed because a significant area of coating layer is absent. A square of width 6 cm and height 6 cm comprising 64 dots without coating layer of 6 mm diameter each has only 50% coated area remaining, so solar performance is sacrificed.
U.S. Pat. No. 7,190,326B2 (PPG/Voeltzel) provides an electrically conductive coating of an automotive heatable windshield, comprising a communication window, i.e. a frequency selective surface (FSS). The FSS comprises passing areas (uncoated areas) and blocking areas (coated areas) to pass and block respectively predetermined wavelengths of the electromagnetic spectrum. Passing areas and blocking areas may be arranged in a number of columns, defined by ablations, spaced from one another by a continuous elongated blocking area. Busbars for supplying heating current to the electrically conductive coating may be oriented above and below the columns so that current flows between adjacent columns to avoid the formation of hot spots. The smaller the distance between adjacent columns, the more the reduction in intensity of hot spots.
DE-102011115967A1 (Daimler/Frosch) discloses advantageous patterns of ablations in an electrically conductive coating in a windshield, resulting in areas of improved transmission at a predetermined frequency. Ablations are interrupted at crossing points so that electrical continuity is maintained, thus electrical heating is not disadvantaged.
It is an object of the present invention to provide an alternative heatable glazing, comprising an area with maintained or improved data transmission and improved uniformity of heating and maintained or improved solar performance, compared with a conventional data transmission window.